The desirability of controlled release of beneficial agents to an environment of use, such as the physiological fluid of animals (e.g. mammals) is known. Controlled delivery of beneficial agents such as drugs can, for example, result in a relatively constant concentration of such agents in the physiological fluids of an animal instead of the more dramatic rises and subsequent decreases in concentration of such agents usually associated with periodic dosing. Furthermore, controlled delivery of drugs can eliminate certain deleterious effects sometimes associated with a sudden, substantial rise in the concentration of certain drugs.
A variety of devices for the controlled delivery of beneficial agents have been described. Certain of those devises employ the physical phenomenon of diffusion for their operation. Examples of such diffusion driven devices are disclosed in U.S. Pat. No. 4,217,898. Other devices have been described which operate with the principle of colloidal osmotic pressure. Examples of such osmotically driven devices are disclosed in U.S. Pat. Nos. 3,845770; 3,995,631; 4,111,202; 4,160,020; 4,439,196 and 4,615,598. Devices which employ a swellable hydrophilic polymer which exerts pressure on a container forcing drug therefrom is disclosed in U.S. Pat. No. 4,180,073. U.S. Pat. No. 4,327,725 discloses a device which employs a layer of fluid swellable hydrogel to force beneficial agent out of the device through a specified and defined passageway. Other hydrogel powered devices containing such a passageway for delivery of beneficial agents are disclosed in GB 2,140,687A.
U.S. Pat. No. 4,350,271 teaches a fluid dispenser that operates by absorbing water. The dispenser includes a rigid water permeable housing, a water insoluble, water swellable composition that fills a segment of the space within the housing, a lipophilic fluid charge that fills the remainder of the space within the housing and that is immiscible in the water-swellable composition, and an outlet through the housing that communicates with the fluid charge. In operation the water swellable composition absorbs water, expands, and in piston-like fashion displaces the fluid charge from the dispenser via the outlet. Finally U.S. Pat. No. 4,434,153 discloses a delivery device comprising a hydrogel reservoir containing tiny pills which include a drug core surrounded by a wall.
Although the above inventions have advanced the art significantly there is a continuing search for other delivery devices particularly those which deliver water insoluble agents.